“[C]laims are given their broadest reasonable construction consistent with the specification. . . . [A]n applicant who has not clearly limited his claims is in a weak position to assert a narrow construction. Therefore, in construing the phrase ‘consisting essentially of’ in appellants’ claims, it is necessary and proper to determine whether their specification reasonably supports a construction that would include additives such as [those in the prior art].” In re Herz, 537 F.2d 549, 551 (CCPA 1976).